The application of machine learning in corrosion data analysis and corrosion prediction has become an important development direction of corrosion discipline in recent years. This paper introduces the application of machine learning in soil, sea water and atmosphere-corrosion research in recent years, compares the machine learning methods and research results for different environments, and summarizes the existing problems of machine learning in the corrosion research of three kinds of natural environments. The future development trend of machine learning in the field of material corrosion is prospected.

Waste-to-energy has become an important means to enter a low-carbon, environmentally friendly society. During the operation of waste boilers, high-temperature flue gas corrosion occurs on their key components such as water-cooled walls and superheaters. In addition, the steam temperature for power plants are also increasing significantly, which may further deteriorate the corrosion and erosion conditions for the boiler heating surface. In this severe corrosive environment, it is very important that on the heated surfaces a dense, uniform and tough coating should be applied, as well as a protective oxide scale should form on their surface to ensure the stable operation of the waste incinerator. As people continue to explore, significant progress has been made in materials and coatings with excellent corrosion resistance, such as alloy 625 overlay welding, induction fusion coating of NiCrBSi, laser fusion coating of cermets, and thermal spraying composite coatings etc. In this paper, on the basis of the introduction of the severe corrosion conditions of waste incineration boilers, the corrosion mechanism of the heating surface of waste incinerators is discussed, the research progress of the protection technology for the heating surface of waste-to-energy boilers in recent decades is reviewed, and the future research direction is prospected.

Zinc 8-hydroxyquinoline (ZnQ₂) bifunctional nanofiller with fluorescent and inhibitive properties was prepared by hydrothermal method, which was added into epoxy resin as a fluorescent indicative primer. Tannic acid-wrapped carbon nanotubes (TA-CNTs) was filled into epoxy resin topcoat to achieve high corrosion resistant. Accordingly, the obtained composite coatings both featured dual-function properties. SEM, FT-IR, XRD, and fluorescence spectroscopy were employed to verify the successful synthesis of fluorescent nanofiller. Corrosion resistance of the composite coatings was confirmed through salt spraying and electrochemical tests. Fluorescence microscopy was applied to evidence the self-indicator of defects on the composite coatings. The results show that the synthesized ZnQ₂ nanofiller is an excellent fluorescent indicator and corrosion inhibitor. After 30 d salt spraying test, the low-frequency impedance |Z|_{0.01 Hz} of the composite coating sustains above 2.95×10⁹ Ω·cm², indicative of high corrosion resistance. When the coating was damaged mechanically, a strong fluorescence emitted under 365 nm under ultraviolet irradiation at the defective areas. Moreover, the fluorescence emitting capability present favorable durability even after 10 d salt spraying test, which would provide promising indication for rapid defect diagnosis and maintenance.

The synergistic effect of walnut green husk extract (WGHE) and rare earth salt Nd(NO₃)₃ on the corrosion inhibition of Al plate in HCl solution was investigated by mass loss method, polarization curve measurement, electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and atomic force microscope (AFM). The mass loss results indicate that the individual WGHE or Nd(NO₃)₃ has moderate corrosion inhibition efficiency, and the maximum corrosion inhibition rate at 25 ℃ is 67.8% and 79.1%, respectively. The synergistic corrosion inhibition will be produced after the two are used in combination, namely the inhibition efficiency_{at 40 ℃ is as high as 90.4% for the combination of 0.5 g/L WGHE and 1.0 g/L Nd(NO3)3. Both WGHE and Nd(NO3)3 were adsorbed on the Al surface to form a protective film before and after the compounding, and the adsorption conformed to Langmuir adsorption isotherm. The compound of WGHE and Nd(NO3)3 can more effectively inhibit the cathodic reaction. The Nyquist plot is approximately "elliptical". After WGHE is combined with Nd(NO3)3, the charge transfer resistance and polarization resistance of the inhibition film on Al further increase, while the constant phase angle component parameters decrease. SEM and AFM characterization results show that the corrosion reaction of the Al surface in the system slows down and the flatness of the Al surface is significantly improved. The major effective components of WGHE mainly are naphthoquinones and flavonoids.}

The effect of pH value, temperature and salinity of seawater on the film formation of B30 Cu-Ni alloy were studied by EIS, XPS and CLSM. The results showed that with the increase of pH value within the range of 6.6-9.8, the film quality first became better and then worse; with the increase of the temperature within the range of 2-36 ℃, the quality of the film became worse first and then better; with the increase of salinity within the range of 20-36, the quality of the film became worse first and then better. The pH and salinity had a strong influence on the corrosion of B30 copper nickel alloy. Therefore, considering comprehensively the corrosion morphology of the alloy and the quality of the corresponding film formed on the surface, can produce the most compact and effective passivation film can be produced on the surface of B30 Cu-Ni alloy in the seawater with salinity of 20.

The effect of hydrogen pre-charging and in situ charging on performance of the charged steel is different due to the diverse interactions between hydrogen diffusion, trapping and dislocation movements for the two processes. In this paper, 304L austenitic stainless steels of different grain size were produced by heavy cold-rolling and annealing treatment, and then their hydrogen embrittlement behavior were investigated by tensile tests, while the testing steels were subjected to either hydrogen pre-charging or in-situ charging. The results showed that, during tensile testing by in situ hydrogen charging, the emerging surface cracks and dislocation movements could increase effective hydrogen diffusivity, meanwhile, the entering hydrogen is absorbed by a large number of grain boundary traps in the steel to homogenize the distribution of hydrogen, which leads to the relative decrease of local hydrogen concentration for each grain boundary. Therefore, grain refinement can inhibit the hydrogen embrittlement tendency of steel during tensile test while dynamic hydrogen charging. On the contrary, a long pre-charging time (96 h) makes a large amount of hydrogen enter the fine-grained steel and store in the grain boundary traps, which increases the concentration of hydrogen in grain boundaries. In the subsequent tensile testing, the grain boundaries serve as a source to supply hydrogen to the newly generated dislocations, resulting in a higher sensitivity of fine-grained steel to hydrogen embrittlement. Indeed, for the steel subjected to pre-charging hydrogen, no evident of decrease in hydrogen concentration of grain boundaries was indicated after grain refinement. As the steel being subjected to pre-charging, each grain boundary contained a high amount of hydrogen, which may act as source for delivery of hydrogen to the newly generated dislocations, therefore, grain refinement enhanced the HE of fine-grained steels.

The long-term corrosion behavior of a novel Cu-Mo test steel in an artificial marine atmosphere was studied by means of dry-wet alternate periodic immersion test, field emission scanning electron microscopy (FE-SEM), field emission electron probe (FE-EPMA), X-ray diffractometer (XRD), Raman spectroscopy (Raman) and electrochemical test. The results show that the Cu-Mo test steel presents a microstructure composed mainly of polygonal ferrite and a small amount of lamellar pearlite, while the counterpart Cr-containing weathering steel presents a microstructure composed mainly of bainite and ferrite. The corrosion process of the Cu-Mo test steel can be divided into two stages: acceleration and deceleration. In the early stage of corrosion, the corrosion resistance of the Cu-Mo test steel is inferior to that of the ordinary Cr-containing weathering steel. At the later stage of corrosion, the enrichment of Cu and Mo occurred in the Cu-Mo test steel, thereby resulted in the increase of α-FeOOH, which enhanced the protectiveness of the rust layer, therefore the corrosion rate of the Cu-Mo test steel decreased. In a word, the new Cu-Mo test steel presents better weathering resistance rather than that of the ordinary Cr-containing weathering steel.

The corrosion behavior of ZAlSi7Mg Al-alloy in low temperature and high pressure deep-sea environment was studied by using a home-made high-efficiency cascade device, whilst the long-term corrosion rate, pitting depth, corrosion morphology and corrosion products of ZAlSi7Mg Al-alloy at depth of 500, 800, 1200 and 2000 m in test sites located in the Western Pacific Ocean and the South China Sea were comparatively assessed by means of SEM, EDS and XPS techniques. The results show that: (1) The corrosion rate and corrosion product thickness of ZAlSi7Mg Al-alloy at 500 and 2000 m depths are higher than those at 800 and 1200 m depths respectively in the Western Pacific Ocean, and the average pitting depth of ZAlSi7Mg Al-alloy gradually decreases with the increase of the test depth. (2) The corrosion types of ZAlSi7Mg Al-alloy in the deep-sea environment are mainly pitting corrosion, crevice corrosion and intergranular corrosion. (3) In the deep-sea environment of the Western Pacific Ocean, the corrosion products of the alloy tested at larger depth have higher Al content, but lower Mg content, in comparison to those tested at shallower depth. The corrosion products mainly include Al₂O₃, Al(OH)₃, Al₂SiO₅ and Mg(OH)₂. (4) The ZAlSi7Mg Al-alloy presents different corrosion behavior, namely its corrosion rate and pitting depth for testing at the same seawater depth in the Western Pacific Ocean and the South China Sea respectively. In the South China Sea, the corrosion rate of Al-alloy at 2000 m depth is slightly less than that at 1200 m depth, while the pitting depth of Al-alloy at 2000 m depth is slightly greater than that at 1200 m depth. However, for the Western Pacific Ocean, change trends of corrosion rate and pitting depth of ZAlSi7Mg Al-alloy in these two depths are just opposite to those in the South China Sea.

Elbow erosion is an important matter related directly to the safe operation of pipeline conveying system and the service life of pipeline. To relieve the harmful effect of this kind of erosion, ribs with different shapes such as quadrilateral, isosceles trapezoid and isosceles triangle sections were designed and prepared, which then were installed at different designed positions in the inner edge on the half side of the elbow with large curvature radius, and the effect of evenly installing multiple ribs on the erosion process was also considered. CFD-DPM method was used to simulate the erosion resistance of the elbow with rib structure. The results show that if the rib is installed just behind the leading edge of the particle impact on the elbow wall, the existence of rib can change the trajectory of the particles, inhibit the erosion to a certain extent, and induce the formation a low-speed counter current circulation zone on behind the rib to protect the elbow wall in this area. Among the three proposed ribs of different cross sections, the isosceles triangular ribs have the best anti-erosion effect. The greater the rib thickness is, the greater the protection range is. However, the rib thickness does affect the impact angle of particles and increase the collision frequency of particles, therefore, a proper rib thickness may be carefully selected for acquiring the better anti-erosion performance. The isosceles triangular ribs with a rib thick in 6 mm have the best anti-erosion effect at θ=25°, which is 43.63% higher than that of ordinary curved tubes. Many ribs evenly installed on the elbow also have obvious anti-erosion effect, in fact, installation of 8 ribs with isosceles triangular cross section have the best anti-erosion performance. The conclusion can provide a new reference for the anti-erosion optimization design of elbow.

Aimming at the Q235 and 40Cr steel samples exposed in air for 1 and 3 a in typical substations in Anhui province, the products and morphologies of their corrosion layers were investigated, and further the corrosion mechanisms were clarified. The corrosion rate of the steel samples was obtained via the mass-loss method, and then the grey correlation analysis was executed to determine the influences of main environmental factors on atmospheric corrosions of the Q235 and 40Cr steel samples exposed for 1 and 3 a, respectively, through combining with the main environmental factor data of the relevant cities in Anhui province. The results showed that the atmospheric corrosion products of the Q235 and 40Cr steel samples were FeOOH, Fe₃O₄, Fe(OH)₃ and FeSO₄. The corrosion layer is covered by cotton ball-like α-FeOOH and flaky γ-FeOOH. It has a dense structure, but laminar cracking takes place. The atmospheric corrosion grades of the Q235 and 40Cr steels in Anhui province have no significant difference, and both are of C2 and C3. The correlation degree sequence of environmental factors affecting atmospheric corrosion of the Q235 and 40Cr samples exposed for 1 a is: NO₂> temperature >SO₂> relative humidity >O₃. With the exposure time prolonging to 3 a, it is changed to be: SO₂, temperature >NO₂> relative humidity >O₃.

In general, certain additives were incorporated into potassium sodium tartrae based electrolyte for electroless copper plating, aiming to improve its stability and the electroless copper plating efficiency. Herewith, L-malic acid and 2,2'-bidipyridine were selected as additives. The effect of L-malic acid and 2,2'-bidipyridine individually or in combination as additives on the performance of the sodium potassium tartrate based electrolyte for copper plating on polyacrylonitrile-butadiene-styrene copolymer (ABS) plates was studied, while the ABS has been subjected to light etching pre-treatment in an optimized MnO₂-H₂SO₄-H₂O ternary solution. The results showed that the addition of L-malic acid increased the Cu-deposition rate, while the addition of 2,2'-bidipyridine decreased the Cu-deposition rate. When the combination additives of 2 mg/LL-malic acid and 1 mg/L2,2'-bidipyridine were added to the potassium sodium tartrate electroless copper plating system, the deposition rate increased from 3.94 µm/h to 5.20 µm/h, and the copper plating system has higher stability. Accordingly, the acquired Cu-coating was uniform, compact and good adhesive to the substrate, and which presents light pink color with a high gloss as well. Finally, a stable low temperature electroless copper plating system was determined in terms of the bath stability, Cu-deposition rate, and the coating morphology and gloss etc.

Aluminide coating was prepared on Ni-base superalloy K444 by chemical vapor deposition (CVD). The oxidation behavior in air at 750, 850 and 950 ℃, and solid Na₂SO₄ induced corrosion in air at 750 ℃ were investigated for K444 alloys without and with CVD aluminide coating respectively. The kinetic curves were obtained. The cross-section morphology and composition of oxidized and corroded samples were characterized by SEM/EDS and XRD. The results show that a continuous and dense Al₂O₃ scale can form on the surface of CVD aluminide coating during oxidation and corrosion, which inhibits the outward diffusion of metal elements, correspondingly, slows down the oxidation reaction and solid Na₂SO₄ induced corrosion, and therefore, significantly enhances the resistance to the high temperature oxidation in air at 750-950 ℃, as well as to the solid deposits of Na₂SO₄ induced corrosion in air at 750 ℃ of K444 alloy.

A pre-chemical conversion film on the inner walls of 70Cu-30Ni alloy pipeline was first prepared with a flowing FeSO₄ solution, and then of which the erosion corrosion behavior in flowing seawater of various speeds was investigated by means of seawater circulation loop. The result showed that a chemical conversion film is obtained during the immersing- and flushing-process of the 200 mg/L FeSO₄ solution in conditions: flowing speed 0.5 m/s, pH 6.0, at 25 °C for 30 d, which is a composite film composed of an inner layer of NiO-Ni(OH)₂, a compact middle layer of Cu₂O-FeOOH and a loose outer layer of Fe₂O₃-FeOOH. Long-term seawater erosion corrosion test results showed that being suffered from flowing sea water of 0.5 and 1.5 m/s, the chemical conversion film covered pipe lines display relative sound anticorrosion performance with only slightly thinning of the top loose layer of the film, while with the increasing seawater flowing rate up to 2.5 m/s the loose layer on top of the conversion film is significantly thinned with locally spalling off, thus exposing the compact middle layer underneath. XPS analysis results showed that the chemical conversion films had been suffered from erosion corrosion of high-speed flowing seawater display higher amount of Ni, Cu₂O and FeOOH on the conversion film surface. Electrochemical impedance results showed that the charge transfer resistances of the chemical conversion films varied in the following descending order: from 2.28×10⁵ Ω·cm², 8.77×10⁴ Ω·cm² to 6.51×10⁴ Ω·cm², after being subjected to erosion-corrosion test by seawater of flowing speeds of 0.5, 1.5 to 2.5 m/s, respectively.

The applicability of hot-dip aluminum (HDA) coating in oilfield reboiler tube bundles is studied by means of micro-morphological observation, polarization curve test, and 240 ℃-salt deposited-CO₂/O₂ multi-degree coupling environment simulation testing in this work. The HDA sample is mainly composed of pure Al outer layer and tongue-shaped Fe₂Al₅ inner alloy layer, and the thickness is between 150 and 200 μm. The polarization curves, which measured at 30 ℃ in simulated oilfield water, show that the corrosion current density of the HDA sample is about 300 times lower than that of 20#, and display excellent corrosion resistance. The simulated results at high-temperature-high-pressure environment show that the uniform corrosion rate of 20# steel in extreme environment is 0.68±0.04 mm/a, the maximum pitting depth is 70.5 μm in 240 ℃-salt deposited-CO₂/O₂ multi-degree coupling environment. In addition, the corrosion scales formed on the surface are consisted Fe₃O₄ and Fe₂O₃, and some cracks can be detected in the scales. However, the corrosion rate of the hot-dip aluminum coating is 0.08±0.02 mm/a, the corrosion mainly occurs in the pure Al layer, and the corresponding corrosion scale is Al(OH)₃ after simulated testing. The comprehensive results show that the hot-dip aluminum coating exhibits excellent anti-corrosion performance under this complex environment.

The corrosion behavior of hot-dip galvanized steel after various test cycles in simulate marine atmospheric environment was assessed by mass loss method, 3D confocal microscope, electrochemical impedance spectroscope (EIS), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD) and X-ray photoelectron spectroscope (XPS). The results show that the corrosion rate of the steel samples was higher at the beginning of the experiment, then decreased at 56 d, and increased again at 104 d, which might be related to the formation of corrosion products. After being tested for 56 d, the steel suffered form mainly uniform corrosion, the main corrosion products were hydroxyzinc chloride (Zn₅(OH)₈Cl₂·H₂O), zinc oxide (ZnO) and basic zinc carbonate (Zn₅(OH)₆(CO₃)₂). In the simulated marine atmospheric environment, the corrosion resistance of the hot-dip galvanized coating failed quickly. Whilst, the corrosion rate has been accelerating until the formation of a relatively complete corrosion product film on the existed damaged areas, hence, the corrosion product film has a certain inhibitory effect on the corrosion of the coating.

The aluminizing process of T92 steel was conducted by slurry aluminizing method. The growth kinetics of the aluminized layer with a slurry layer thickness of about 80 μm at 700 ℃ was tested. The surface and cross-sectional morphology and composition of the aluminide coating were characterized by using SEM, EDS and XRD respectively. The results show that the active Al atoms ([Al]) diffused inward to form Fe₂Al₅ (η) phase in the first three hours of aluminizing. Then [Al] began to accumulate at the interface of the slurry/the formed aluminide coating, while Fe diffused outward rapidly resulted in the formation of the outer portion of the coating composed of mixed-phases Fe₂Al₅ (η) and FeAl₃ (θ). After 10 h, the inner portion of FeAl (B2) phase could be clearly observed in the aluminized coatings. The mechanism of aluminized coating growth process and the relevant diffusion process of metallic components was discussed from the point of view of kinetics and thermodynamics. The thickness of the η-phase layer formed by the diffusion of [Al] with time can be expressed by equation of x=18.40t^1/2-4.80.

The high temperature corrosion behavior of F22 base metal and weld at 510 ℃ in simulated coastal atmosphere was studied. The corrosion kinetic curves of base metal and weld was measured. The microstructure, chemical composition, phase constituent, surface and cross-sectional morphology of corrosion products were characterized by means of optical metallography, XRD and SEM/EDS. The results showed that both the weld and base metal of F22 steel showed mass gain during the corrosion process. The mass gain rate in the initial 250 h is faster than that in the subsequent corrosion process, while the corrosion rate of the weld is slightly greater than that of the base material. The kinetics followed parabolic law after 250 h corrosion. The corrosion product scale had a duplex microstructure, the outer layer was Fe₂O₃, and the inner layer was a mixture of Fe₂O₃, Fe₃O₄. Due to the low Cr content of the alloy, a protective Cr₂O₃ film did not form on the sample surface. The corrosion mechanism is briefly discussed too.

In this article, the tensile fracture behavior of L80 steel in air at 25-350 ^oC and its high-temperature and high-pressure corrosion behavior in CO₂/H₂S in an artificial formation water at 150-350 ^oC are investigated by means of mass loss measurement, scanning electron microscopy, X-ray photoelectron spectroscopy. The results suggest that the yield strength and tensile strength of L80 both appear to severe decline with the increasing temperature, while the decay of the former is significantly greater than that of the latter. Meanwhile, the tensile fracture mechanism of L80 steel changes from microporous aggregation with shear tearing at room temperature to a dominant microporous aggregation at high temperatures. The corrosion rate increases significantly with the increasing temperature, and the higher the temperature, the faster the increase rate. The bilayer structure of the corrosion products and their crystal morphology are markedly affected by temperature, and the percentage of FeS in the inner layer and the compactness of FeCO₃ of the outer layer both increase with the increasing temperature. The results of the study may provide a reference for the evaluation of the adaptability of L80 oil casing for service in extreme conditions.

The corrosion condition of ultra-deep oil- and gas-wells is simulated via a high-temperature and high-pressure reaction kettle that can adjust the temperature, H₂S- and CO₂- partial pressure of the artificial formation waters. The corrosion characteristics of P110SS steel in the artificial formation water by varying temperature, and H₂S- and CO₂-partial pressure, was assessed by means of immersion test, SEM, EDS and XRD. The results show that the corrosion rate of P110SS increased with the increase of H₂S and CO₂ partial pressure, but decreased with the increase of temperature. By analyzing the corrosion products, it is found that the change of H₂S-, CO₂- partial pressure and temperature will lead to the change of composition and structure of corrosion products. This shows that under the condition of high temperature and high pressure, the corrosion of H₂S is dominant, the corrosion product of Fe₇S₈ has poor protectiveness and thus the steel presents high corrosion rate, and the corrosion of CO₂ is dominant under the condition of low H₂S partial pressure, the corrosion rate depends on the compactness of the corrosion product film. However, the effect of temperature on the corrosion rate is more significant than that of CO₂.

To promote the rapid development of green plant extract inhibitor, navel orange peel extract (NOPE) was obtained by a simple ethanol-acetone reflux method, which then was assessed as inhibitor for 316L steel in hydrochloric acid medium. The main components of navel orange peel extract (NOPE) and its stability in hydrochloric acid were confirmed by infrared spectroscopy (FTIR) and ultraviolet spectroscopy (UV). The corrosion inhibition performance of NOPE to 316L steel in 0.5 mol/L HCl solution was investigated using mass loss method, dynamic potential polarization method (PDP), linear polarization method (LPR) and electrochemical impedance spectroscopy (EIS). Their adsorption properties were calculated with items of \mathrm{\Delta }{G}_{\mathrm{a}\mathrm{d}\mathrm{s}}^{\mathrm{0}}, \mathrm{\Delta }{H}_{\mathrm{a}\mathrm{d}\mathrm{s}}^{\mathrm{0}} and \mathrm{\Delta }{S}_{\mathrm{a}\mathrm{d}\mathrm{s}}^{\mathrm{0}}. The results show that with the increase of the concentration of NOPE, the steel corrosion rate is reduced, the anode current is reduced and the active corrosion site is blocked, so the inhibition efficiency is improved. When the concentration of NOPE was 0.5 g/L, the maximum corrosion inhibition efficiency was 90.5% (masslessness method) and 87.3% (electrochemical method) respectively. Compared with the blank system, the thermodynamic activation parameter (activation energy) E_a significantly increased in the system with NOPE, and the difference of (E_a-\mathrm{\Delta }{H}_{\mathrm{a}}^{\mathrm{0}}) was about equal to the average value of RT (2.64 kJ/mol). Therefore, it can be inferred that the corrosion process was a single molecule reaction. The adsorption process on the steel surface was fitted by Langmuir isotherm, which further proved that the adsorption was monolayer adsorption. The better corrosion inhibition performance of NOPE for L316 steel in 0.5 mol/L HCl solution system can also be proved by the observation and detection with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In sum, the NOPE is a green inhibitor with a good application prospect in the field of pickling and can provide certain guidance for the development of plant extract inhibitor.

Electrochemical properties and real-sea corrosion behavior of duplex stainless steel SAF 2304 in a test site located in the Zhoushan area of the East China Sea, with a depth of about 10 m were assessed by mean of mass loss measurement, electrochemical tests, optical microscopy (OM) and scanning electron microscopy (SEM) and compared with carbon steel. The electrochemical test results show that the free corrosion potential of carbon steel is -0.857 V_SCE, the passive current density is 87.30 μA‧cm^-2, the capacitive arc radius is small, and the corrosion resistance is poor. SAF 2304 duplex stainless steel is stable for a long time in the open circuit potential of 3.5%NaCl solution, the free corrosion potential is -0.369 V_SCE, the passive current density is 18.03 μA‧cm^-2, the capacity of the arc resistance is large, and the corrosion resistance is good. In the real sea exposure experiment, the corrosion rate of SAF 2304 duplex stainless steel is much smaller than that of carbon steel. With the increase of exposure time, a relatively compact scale composed of Ca and Mg containing deposits and SiO₂ may further form on the pre-formed metal oxide film, and all the corrosion products are tightly adhered to the substrate, therefore, provides protective effect to a certain extent for the steel, and the corrosion morphology is uniformly corroded.

Suppression of secondary phase precipitation is crucial for the improvement of hot-working character and corrosion resistance of super austenitic stainless steels (SASS). In this paper, a composite heat treatment process of dynamic solid solution treatment followed by low temperature aging was named the new heat treatment process, through which the alloying elements such as B distribution of steels can be adjusted. Hence, the effect of the new heat treatment process on the second phase precipitation and corrosion resistance of S31254 SASS was studied by means of SEM and EDS as well as CS350 electrochemical workstation. The results show that the new heat treatment process can suppress the formation of the second phase precipitation and change the distribution of alloying elements of the steel. The content of Mo in the precipitates of the sample steels 0B and 40B after treated by the new heat treatment process was much higher than those treated by the conventional solution treatment, which can result in the reduction of the total amount of precipitates and the improvement of the hot workability of the steel. The intergranular corrosion susceptibility of the sample steels treated by the new heat treatment process was evaluated by double ring potentiodynamic activation test (DL-EPR), which confirmed that the new heat treatment process can further improve the intergranular corrosion resistance of the sample steel 40B containing 0.004%B.

The effect of chemical conversion coatings Ca-P and Sr-P on the corrosion resistance of Mg-Zn-Zr-Gd alloy, which was solidified by pulsed magnetic field and then cast, was studied by means of immersion test, electrochemical measurement, scanning electron microscopy and other methods. This investigation revealed that the corrosion resistance of the substrate sample, which was solidified by pulsed magnetic field, was better than that of the substrate sample, which was solidified without pulsed magnetic field, and the corrosion resistance of the substrate sample has a certain influence on the corrosion resistance of the coating, the better the corrosion resistance of the substrate sample, the better the corrosion resistance of the coating prepared on the surface. In addition, different chemical coatings have different corrosion resistance, the Ca-P coating was composed of a large number of rod-shaped particles, which were unevenly distributed and relatively loose, and the thickness was non uniform, the observation of corrosion morphology of the Ca-P coating showed that loose corrosion products with large number of voids were formed in the coating. The Sr-P coating was composed of many fine granular with uniform thickness, the corrosion products of the Sr-P coating were relatively dense, which hindered the possibility of further corrosion of the alloy. The results showed that both Sr-P and Ca-P coatings can improve the corrosion resistance of the substrate, and the corrosion resistance of the Sr-P coating was better than that of the Ca-P coating.

The effect of heat treatments on the corrosion behavior of low carbon steels with 3%Cr (mass fraction) in Cl^- containing environment was assessed by means of immersion test, electrochemical measurements, scanning Kelvin probe (SKP), and atomic force microscope (AFM). Results show that annealing leads to single ferrite microstructure, and normalizing causes duplex microstructure consisting of ferrite and bainite. The microstructure difference is the intrinsic reason for the corrosion morphology difference in the initial corrosion stage. In the contrast to the microstructure of annealed steel, the existence of two phases in the normalized microstructure causes galvanic effect, which then resulted in lower corrosion resistance of the steel.

For improving the copper anode corrosion uniformity and the current efficiency of the copper electrolytic refining process, herewith, based on the multi-physical field coupling theory, the corrosion behavior of the copper positive plate of the copper electrolytic refining cell was studied in terms of the effect of the synergy of the stress and strain, and local corrosion reaction, as well as the bottom radius of the anode plate on the positive electrode corrosion current density distribution and the thinning uniformity of the anode plate. The results show that when the bottom fillet radius of the anode increases from 2 mm to 12 mm, the current density mutation rate on the anode plate decreases by 6.18%. The uniformity of anode thinning rate was improved by 43.44%. When the fillet radius is 8 mm, the current efficiency is the highest, reaching 99.18%. By optimizing the geometrical shape of electrode plate, the uniformity of thinning rate and current efficiency of the anode plate are effectively improved, which provides a theoretical guidance for further optimizing the structure of electrolytic cell for reducing energy consumption, as well as improving the thinning uniformity of electrode plate.

The hot corrosion behavior in molten salt (75%Na₂SO₄+25%K₂SO₄) at 850 ^oC of Hastelloy X alloy made by additive manufacturing was studied, and then the room temperature mechanical properties of the alloy after molten salts corrosion were also assessed. The results show that the corrosion products of Hastelloy X are mainly composed of Ni-, Ti- and Cr-oxides. After hot corrosion for different times, the tensile strength of the additive manufactured alloy at room temperature changes little, while the rupture strength and plasticity decrease significantly, which may be ascribed to the change of the surface state and structure of the alloy induced by the molten salts corrosion process in terms of the effect of temperature and corrosion.

The corrosion behavior of Q235 steel was studied by outdoor exposure and under the shelter of an awning respectively in the same atmosphere at one test site located at the coastal of Hainan island in the South China Sea by means of mass loss method, electrochemical test methods, macro-morphology, cross-sectional micro-morphology, and X-ray diffractometer (XRD) etc. The results showed that the color of corrosion products on the surface of Q235 steel by outdoor and under the shelter all gradually darkens with time, and however the darkening rate for the steel under the shelter was faster than that by outdoor exposure. The corrosion products gradually changed from FeOOH to Fe₂O₃ and Fe₃O₄.The transformation trend of the steel by outdoor exposure was slower than that under the shelter. As a result, a thick corrosion product with many cracks and pores may emerge, therefore its protectiveness for the substrate might be deteriorated, so that the corrosion rate of the steel was rose. The mass loss analysis showed that the corrosion rate for the steel by outdoor exposure was much higher than that under the shelter, and the annual average mass loss rate of the former was about 2 times of that the later. The results of electrochemical test show that the R_p of the steel by outdoor exposure is less than that under the shelter, which indicates that the corrosion tendency of the steel by outdoor exposure is greater than that under the shelter. The main reason is that the air humidity is relatively low, the sunlight is sufficient, the salt concentration is higher, and the residual salt concentration on the surface of the steel is also higher by the outdoor exposure, which leads to the deterioration of the corrosion condition.